well its exactly the same except for a few details
MF has a facing requirement so its not always ideal when multidotting
MF does damage for your GCD while SWPain does not
MF costs less mana
MF Stacks evangalism
MF can proc more orbs

MF refresh has the same effect as a hard cast on the dot damage but will always be a dps gain over hard-casting. Ideally you should hard-cast SWPain once per target per fight (for 2-3 target fights, more than that and it gets hard to keep em all up with just MF).